This invention relates generally to breath alcohol testing and, more particularly, to a sampling system and fuel cell configuration for a breath alcohol tester.
Known breath testers include a sampling assembly, fuel cell assembly, and electronics/software for determining an amount of alcohol in a sample, based on a signal generated by a fuel cell. More specifically, the sampling assembly functions to deliver a controlled volume breath sample to the fuel cell assembly, and the fuel cell generates a signal representative of the amount of alcohol in the delivered sample. The fuel cell should react quickly and completely to the introduction of an alcohol sample of controlled volume, and produce electrons with repeatability in response to the reaction with the alcohol. The number of electrons produced is proportional to the concentration of alcohol consumed by the reaction. The signal generated by the fuel cell is processed by the electronics/software to determine alcohol concentration.
At least some known sampling assemblies include a pump connected to the fuel cell assembly via a tube. The pump pulls a breath sample into the fuel cell housing through a sampling port, across the face of the fuel cell, and out the opposite side of the housing, through the pump, and into the ambient air. Other known sampling assemblies include a cylinder and piston directly attached to the fuel cell assembly. Within such configurations, the sampling assembly and the fuel cell assembly are coupled together in flow communication via a small opening, such that the piston draws a breath sample into the fuel cell, through a sampling port, and into the cylinder, through the small opening. More specifically, within such a configuration, the fuel cell assembly includes two ports and is sometimes referred to as a bypass system.
However, with at least some known bypass systems, it may be difficult to ensure that a consistent and approximately equal volume is sampled each time because of the pump or piston operation. Moreover, with at least some bypass systems, it may be difficult to ensure that 100% of the alcohol in the sample is consumed by the fuel cell during a measurement. As such, any alcohol that originally bypassed the fuel cell going through the fuel cell may start a new reaction in the fuel cell upon reset, thus extending the time between subsequent tests.
In another known configuration, the sampling assembly is directly connected to the fuel cell assembly, and the sampling assembly includes a moveable element, such as a diaphragm. When the sampling assembly is attached to the fuel cell assembly, the diaphragm functions as a moveable wall of the fuel cell housing. Accordingly, when the diaphragm moves in one direction, a breath sample is drawn into the fuel cell assembly, but not through it. This type of assembly in which the fuel cell assembly has only one port is sometimes referred to as a dead-end system.
However, with at least some known dead-end systems, when diaphragms are used, the diaphragm assumes its natural molded shape in the “sample” position, such that when the diaphragm is in the reset position, stresses may be induced into the diaphragm material depending on the material. Over time, such stresses can alter the shape of the reset diaphragm which may adversely affect the long term calibration of the sampling assembly.